Numerous devices are known for transmitting heat from one fluid to another in which the two fluids do not contact one another or become mixed. However, most of these devices are not directly applicable to a solar heated receiver wherein radiant thermal energy is transferred to a fluid. For example, U.S. Pat. No. 1,796,945 discloses a heat exchanger wherein two spaced-apart tube plates are inclined with tubes extending between the two plates and having one end attached to the upper plate. The fluid to be heated passes along the outside of the length of the tubes.
U.S. Pat. No 2,252,069 also relates to a heat exchange apparatus and is particularly concerned with tubular connections through which liquid or fluid is introduced into pressure vessels such as a vapor generator. The invention disclosed therein provides tubular connections which are particularly applicable to high pressure boilers wherein the feed from an economizer to a steam or water drum of the boiler varies widely in temperature due to operating conditions beyond the control of the designer.
U.S. Pat. No. 3,286,767 provides a tube support arrangement for use in a heat exchanger tube bundle. It specifically describes a tube support spacer for use in a tube bundle comprising a plurality of nested helical tube coils wherein the tube support arrangement provides support for the tubes both in a horizontal and a vertical direction while permitting relative differential expansion between adjacent coils of tubes.
U.S. Pat. No. 3,896,771 discloses a spacer and guide assembly for vertical superheater tubes. The spacer and guide assembly include a horizontal tube and guide lug means which are integral with the vertical tubes, and spacer lug means which are integral with the horizontal tube and coacting with the guide lug means so as to permit relative movement of the tubes. The guide lug means and spacer lug means are so related to each other that limited relative movement between the vertical and horizontal tube causes rubbing or contacting action between the spacer lug means and the guide lug means but not between the vertical and horizontal tubes or between either of the tubes and the spacer lug means or guide means.
U.S. Pat. No. 4,123,994 relates to an apparatus for suspension of a tube wall. It particularly relates to a combustion chamber wall in which the tube wall is made of finned tubes welded gas-tight with one another and extend horizontally or inclined, for example, helically-formed wound finned tubes on a steam generator. The proposed apparatus comprises a combination of tie rods interconnected to the helically formed wound finned tubes by means of welding bridges which permit the tie rods to expand in width independent of longitudinal expansion of the finned tubes.
The principal problem with most of the prior art heat exchange devices, however, is they are intended for transfer of heat from one fluid to another. Thus, they are not directly applicable to a solar heated receiver wherein the heat transfer is effected by radiation and wherein one side of the thermal receiver may be at a substantially higher temperature than the opposite side. Further, during the course of the day, a solar heated thermal receiver is subject to extreme heat flux variations from the collectors or heliostats ranging from the cool ambient morning temperatures to the peak daytime temperatures. Still further, the large size of a central solar receiver presents additional difficulties in that the expanse of metal is so great that the temperature differences result in significant changes in size; and the likelihood of excessive stress being applied to connections as a result of such changes is greatly enhanced.